Liquid crystal display (LCD) devices typically include an LCD panel having a liquid crystal layer sandwiched between a thin-film transistor (TFT) substrate and an opposing substrate. The TFT substrate has an array of TFTs for controlling respective pixels of the LCD panel to control the amount of light passing through the liquid crystal layer. The TFTs are coupled to signal lines, scan lines and data lines, where scan lines are used to turn corresponding TFTs on and off, while data lines are used to apply voltages to respective pixels.
During manufacture of an LCD panel, a signal line defect can occasionally occur. For example, FIG. 1 shows a substrate 200 containing an array of TFTs corresponding to an array of pixels of the LCD panel. As depicted, the array of TFTs are driven by signal lines, including scan lines (running in rows horizontally in FIG. 1) and data lines (running in columns vertically in FIG. 1). In the example of FIG. 1, a defective signal line (in this case a defective data line) has a defect 108, which is a break in the signal line. As a result of the break defect 108 in the defective signal line, two signal line portions 120 and 130 in the defective signal line are disconnected and separated from each other. Although the signal line portion 120 still may be used for transmitting signals sent out by a signal driver 102 (since the signal line portion 120 remains connected to the signal driver 102), the other signal line portion 130 is electrically isolated from the driver 102 due to the break defect 108. As a result, the section of the LCD panel (that corresponds to signal line portion 130) cannot display properly, which will adversely affect the image displayed by the LCD panel.
A conventional solution for repairing a break defect is shown in FIG. 2. In FIG. 2, 208 indicates a signal line break defect in a defective signal line on a substrate 200 containing an array of TFTs driven by scan and data lines. Due to the signal line break defect 208, the defective signal line has two disconnected signal line portions 220 and 230. Note that the defective signal line is driven by a signal driver 202. To repair the defective signal line, laser melting can be used to electrically connect the signal line portion 220 and a lead 240 at the intersection 210 of the signal line portion 220 and the lead 240 (note that the lead 240 is provided in a separate metal layer than the defective signal line). Laser melting refers to using laser to cause an opening to be formed through an electrically insulating layer between the defective signal line and the lead 240, such that melting of electrically conductive material of the defective signal line and/or lead 240 will cause a flow of the electrically conductive material into the opening in the electrically insulating layer. As a result of the laser melting (or laser bonding) procedure, the lead 240 is electrically connected to the signal driver 202.
In this manner, the lead 240 transmits the output signal of the driver 202 to a line 205, which can be on a printed circuit board 251. The lead 240 is electrically connected to the line 205 through another lead 245, which can be a lead provided by the package (e.g., COF or TCP) of the driver 202. The signal through the leads 240, 245, and line 205 is provided to the input terminal of a buffer 214. The output terminal of the buffer 214 is connected to a line 215 (running vertically along a side of the TFT array in FIG. 2), which is in turn connected to a line 270. The line 270 runs horizontally along the bottom side of the TFT array, and is located at the ends of the data lines on the substrate 200 (at the ends of the data lines opposite to the ends of the data lines driven by corresponding signal drivers). At the intersection 212 of the line 270 and the signal line portion 230, laser melting is used to electrically connect the signal line portion 230 and the line 270. In this manner, the output terminal of the buffer 214 is electrically connected to the line 270, such that the output signal of the signal driver 202 is able to reach the signal line portion 230 (that was isolated from the driver 202 by the break defect 208). The leads 240, 245, lines 205, 270, and buffer 214 provide an alternate (or repair) path from the signal driver 202 to the signal line portion 230. As a result, the signal line defect 208 can be repaired during the manufacturing process of the LCD panel.
In FIG. 2, note that signal drivers are further associated with corresponding leads 240A, 240C, 240D, 240E, and so forth.
With the arrangement depicted in FIG. 2, parasitic capacitance is formed between leads 240, 240A, 240B, 240C, 240D, and 240E and the data lines of the TFT array in the LCD panel. Also, parasitic capacitance is formed between the leads 245 (provided by the packages of the drivers 202), the line 205 on the printed circuit board 251, and the periphery leads. Therefore, as shown in FIG. 2, there are relatively large parasitic capacitances in the repair path from the output terminal of the signal driver 202 to the input terminal of the buffer 214. As a result, the output signal of the signal driver 202 transmitted to the input terminal of the buffer 214 is delayed and deformed (e.g., reduced rise and falls times), which can affect the quality of the displayed image by the LCD panel that has been repaired. One way to solve this problem is enhancing the driving ability of all the output stages of the signal drivers. However, to do so, the size of the signal drivers will have to be enlarged, which leads to increased manufacturing cost, power consumption, and electromagnetic interference.